Why hatchery-born salmon struggle to spawn in the wildResearch on Oregon rivers shows they get domesticated in as little as one generation

John McMillan, courtesy of Oregon State UniversitySteelhead trout, part of the salmon family, travel from the ocean to freshwater to spawn.By Stephanie Pappasupdated 12/20/2011 6:15:00 PM ET

Salmon born in captivity become domesticated in as little as one generation, a new study finds, explaining why hatchery-born fish don't do as well as wild-born ones in Oregon rivers.

Researchers created an enormous fish family tree using genetic samples from 12,700 steelhead trout (which are in the same family as salmon) returning from the sea to Oregon's Hood River to spawn. This fishy pedigree revealed the fish that spawned well in hatcheries had offspring that spawned poorly in the wild.

"They're adapting to captivity in a single generation," study scientist Mark Christie, a postdoctoral researcher at Oregon State University, told LiveScience. In other words, the fish rapidly became domesticated, Christie and his colleagues reported Monday in the journal Proceedings of the National Academy of Sciences.

"It's similar to the process by which wolves were transformed into dogs," Christie said. "That's all that's occurring here, except it's occurring at a really rapid time scale."

Saving salmonSalmon are considered anadromous fish, meaning they hatch in freshwater streams and rivers, travel as juveniles to the oceans, where they mature into adults and return to their birthplace to spawn and die. Steelhead are actually an anadromous type of rainbow trout, part of the salmon family.

To increase threatened salmon populations in the Pacific Northwest, wildlife managers release more than 6 billion hatchery-born fish each year. But these fish reproduced at about 80 percent the rate of their wild-born brethren, Christie said, raising fears that the influx of hatchery salmon might affect the gene pool and harm the population as a whole.

To understand the problem, Christie and his colleagues needed to find out why these hatchery-born fish lag behind on the reproductive front. Fortunately for their research, high dams block spawning fish from making it upstream in the Hood River on their own. As a result, the fish must be "passed over" the dam in what is essentially an aquatic elevator. This gives Oregon Department of Fish and Wildlife officials an opportunity to get a DNA sample from every fish that returns from the sea to spawn.Advertise | AdChoices

Using these DNA samples, Christie and his co-researchers traced the family relationships of 19 years of threatened Oregon steelhead (Oncorhynchus mykis), which unlike most salmon can survive multiple years of spawning. They found when fish produced higher-than-average numbers of offspring in the hatchery, the offspring of those offspring had just 71 percent the number of babies as fish born in the wild. In other words, whatever it is that makes baby fish thrive and survive in the hatchery is not beneficial in the real world.

Rapid adaptionThe researchers also found that when hatchery-born fish were used to breed new generations in the hatchery, they produced more offspring than wild-born fish breeding in captivity. The two results together mean that the hatchery environment is putting strong evolutionary pressure on the fish, causing them to adapt rapidly — and to lose the strengths that help them in the wild.

"It's probably not just a single trait that is being selected upon," Christie said. "It's probably a lot of traits. When you sum up across all those traits you can get a rapid reduction in fitness."

The researchers aren't yet sure what specific genetic changes occur in hatchery-born fish that make them ill-suited for reproduction in the wild. One possibility, Christie said, is that hatchery fish grow quickly and head out to sea after one year of life. Wild fish are slower to develop, and spend several years in fresh water before heading to the ocean.

The researchers are now digging deeper into the fish genomes to uncover the differences between wild- and hatchery-born steelhead DNA.

"Now that we know what is causing this, we can focus on figuring out specifically what in the hatchery is going on," Christie said. "Once we get there, we'll be able to make more informed management decisions."

You can follow LiveScience senior writer Stephanie Pappas on Twitter @sipappas. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.

Thanks for posting. Very interesting.I would now like to see this done with Pacific Salmon...It probably has...with Cultus Lake SockeyeHopefully one day.....It would be nice to see some research published on what they are finding.

The researchers aren't yet sure what specific genetic changes occur in hatchery-born fish that make them ill-suited for reproduction in the wild. One possibility, Christie said, is that hatchery fish grow quickly and head out to sea after one year of life. Wild fish are slower to develop, and spend several years in fresh water before heading to the ocean.

--For each of these issues there are possible solutions....why not put the fish out in the "wild" at an earlier stage of life... these are mostly bean counter measures of most efficient cost per fish... putting fish back into .. more natural environment.. means less survive and those that do would have much more similar behavioural characteristics that those born in the wild would. The bean counters look at # of fish survive and size when released per amount of food given to explain how cost effective their program is. --For every hatchery ill there are studies that will indicate there are technical fixes to these issues. It is obvious to me without doing a study that if you create a hatchery environment which has no similarity to nature and then you baby the fish to ensure many more survive that would in nature that there would be many weaker survivors thus likely they would not thrive as well in the wild.

It would be interesting to see research done on a river that is almost 100% hatchery like the Cap - if what they are saying in the article, then theoretically each subsequent year it would take more and more smolts to produce at the least an equal number of returning adult fish as the previous year...then again there would be no control group as the cap doesn't have any true "wild" fish - only those that spawn in brothers which may or may not be just fish once removed from their hatchery parents.

If hatcheries were to release fish earlier like another member said, it would be counter productive to the hatchery as the survival would be very close to the wilds and hence no point?

If hatcheries were to release fish earlier like another member said, it would be counter productive to the hatchery as the survival would be very close to the wilds and hence no point?

--The difference is in higher % of initial survival as you reduce chance that egg will be eaten by other fish or dug up by subsequent spawner etc.--Just a note in many of these USA cases the original spawning river and population has been flooded by the dam thus there is no natural stream channel to rear... I am of no illusion that we can completely mimic nature just that we can do a better job than has been given in the examples.

At an 80% success rate the genetics of these hatchery fish will die out in a few generations. The survival difference between a successful variant and an ultimately unsuccessful variant is often far less than that. So don't worry about hatchery stocking, the wild strain will continuously reassert itself through natural selection, even from hatchery stock that spawns naturally. In the meantime we can have better fishing through hatcheries.

At an 80% success rate the genetics of these hatchery fish will die out in a few generations. The survival difference between a successful variant and an ultimately unsuccessful variant is often far less than that. So don't worry about hatchery stocking, the wild strain will continuously reassert itself through natural selection, even from hatchery stock that spawns naturally. In the meantime we can have better fishing through hatcheries.

I may be mistaken but I see it differently. Since tone is hard to tell on the internet, let me start by saying what I type next is purely inquisitive.

Wouldn't this be the case only if you hold everything else equal. The fact is each year hatchery fish are being introduced and when they breed with wild fish they are introducing their genes into the wild "successful variant". This is not natural selection, if anything it is the opposite where the weaker strains are given a better chance to survive through the hatchery program and since they have a higher success rate in the first generation, they are diluting the natural gene pool. Your argument would be true if they completely stopped the hatchery program and the hatchery fish and their progeny died off.